Monarchs and milkweed, at a glance

Some facts about monarch butterflies and the milkweed plants they need to survive:

THE BUTTERFLY

—The migratory monarch population that overwinters in central Mexico from eastern Canada and the U.S. declined 84 percent between 1997 and 2014. A similar decline was observed for the smaller population of migrating Western monarchs that winter in California.

—Threats to the monarchs come from many quarters, among them loss of milkweed habitat in the U.S. and Canada, climate change that may render portions of the central Mexican wintering grounds unsuitable over the next 40 years, insecticides used for mosquitoes, and herbicides used in corn and soybean fields.

—Monarchs breed throughout the U.S. and southern Canada from spring to fall; several generations are produced each year. It takes multiple generations to complete a cycle of migration between Mexico and northern breeding grounds.

—Monarch caterpillars and butterflies gain protection from predators thanks to the sour sap they consume from milkweed leaves.

THE PLANT

—Milkweed is a powerhouse for pollination , supplying high-quality nectar to bees, hummingbirds, beetles and butterflies, and it's the only larval host plant for the monarch butterfly

—Native Americans used milkweed floss for string, rope and cloth and its sap to treat bee stings, ringworm and warts.

—During World War II, buoyant milkweed floss filled life preservers and schoolchildren gathered the pods to help the war effort. In an Illinois program , children were paid 15 cents per onion sack full of pods, more if they were dried. It took two sacks to fill one life jacket.

—It's toxic to cows and other livestock, which avoid eating it unless forage is insufficient in fields with plenty of milkweed.

—It's great for wasps, flies and beetles because they have short tongues and can reach the nectar.

—Best produced from seed, it takes two or three years to produce the first pods filled with floss that is now being marketed in Quebec for clothing insulation and other commercial uses.